Gas turbine engines include fuel systems of a number of kinds, which are fed fuel from a fuel source via internal inlet tubes or passages. Internal fuel manifolds make up part of one such fuel system, and are typically configured as a manifold ring having a fuel inlet tube attached thereto. The fuel inlet tube provides fuel flow into the ring portion of the internal fuel manifold via one or more fuel channels formed within the inlet tube. Gas turbine engine fuel inlet tubes are most commonly circular in cross-sectional shape, generally for ease of manufacturing and installation. In order to create two discrete fuel passages within such an inlet tube having a circular cross-section, two circular holes are typically drilled side-by-side within cylindrical stock material. It is common to have a primary and a secondary fuel passage, having different diameters. The diameters of the two fuel passages are determined based on several factors, including desired pressure drop and flow rate. However, when the fluid dynamic requirements force one or both of the two passages to be of a relatively large size, the overall diameter of the entire inlet tube must necessarily be increased accordingly in order to maintain acceptable wall thicknesses. This proves to be undesirable, given the tight space envelope available for the inlet tube within the engine.